Mast assembly for forklift truck

Abstract

A mast assembly for a forklift truck includes a plurality of guide units. At least one of the guide units includes a sliding pad member made of a plastic material and having a block-shaped body, which is hollow, is open at its base side, and has a rectangular ring-shaped cross section. The sliding pad member has a rectangular, plain, front wall provided at the side of the block-shaped body opposite to the base side thereof. The front wall has a sliding contact surface. Reinforcement ribs are formed on the inner surface of the front wall. Grooves are formed in the sliding contact surface, extending along the respective ones of the reinforcement ribs and helping avoid formation of shrinkage depressions in the sliding contact surface. The block-shaped body includes first and second pairs of opposing side walls. Tabs are formed on the first pair of opposing side walls.

What is claimed is: 
     
       1. A mast assembly for a forklift truck, comprising:
 an outer mast including a pair of right and left uprights each mounted upright on the front of a truck frame of the forklift truck and each having inner guide surfaces; 
 an inner mast including a pair of right and left uprights each received in the corresponding one of said pair of right and left uprights of said outer mast for elevational movement and each having inner guide surfaces and outer guide surfaces; 
 a carriage assembly having a pair of right and left bracket plates each received in the corresponding one of said pair of right and left uprights of said inner mast for elevational movement; 
 a first guide unit fixed onto said inner guide surfaces of each said upright of said outer mast and being in contact with said outer guide surfaces of the corresponding said upright of said inner mast so as to guide said inner mast for elevational movement; 
 a second guide unit fixed onto said outer guide surfaces of each said upright of said inner mast and being in contact with said inner guide surfaces of the corresponding said upright of said outer mast so as to guide said inner mast for elevational movement; and 
 a third guide unit fixed onto each said bracket plate and being in contact with said inner guide surfaces of the corresponding said upright of said inner mast so as to guide said carriage assembly for elevational movement;
 wherein at least one of said first, second, and third guide units comprises a sliding pad member made of a plastic material, and said sliding pad has a hollow, block-shaped body, which is open at its base side, said block-shaped body including a rectangular plain front wall provided opposite to said base side, and a first pair of opposing side walls and a second pair of opposing side walls; and 
 
 the front wall has an inner surface and an outer surface, the outer surface defining a sliding contact surface which is in sliding contact with one of said outer guide surfaces of said pair of uprights of said inner mast, said inner guide surfaces of said pair of uprights of said outer mast, and said inner guide surfaces of said pair of uprights of said inner mast; 
 and the sliding pad member further includes a pair of reinforcement ribs formed on the inner surface of said front wall and extending along diagonal lines of the rectangular sliding surface and crossing at the center of the rectangular sliding surface, and 
 the block shaped body includes a pair of ring-shaped tabs, where one tab is formed within each wall of the first set of opposing side walls of said block-shaped body, said tabs each having a through hole for receiving a screw for fixing said block-shaped body onto one of said inner guide surfaces of said pair of uprights of said outer mast, said outer guide surfaces of said pair of uprights of said inner mast, and the surfaces of said pair of bracket plates, and the head of the fixing screw is at a level lower than that of the sliding contact surface. 
 
     
     
       2. A mast assembly for a forklift truck according to  claim 1 , wherein:
 said sliding pad member comprises a pair of grooves formed in said sliding contact surface for holding therein a lubricant. 
 
     
     
       3. A mast assembly for a forklift truck according to  claim 2 , wherein:
 said sliding pad member has a single, plain surface extending along the entire periphery of a base side of said block-shaped body, which is adapted to be in secure contact with one of said inner guide surfaces of said pair of uprights of said outer mast and the surfaces of said pair of bracket plates. 
 
     
     
       4. A mast assembly for a forklift truck according to  claim 1 , wherein:
 said sliding pad member has a single, plain surface extending along the entire periphery of a base side of said block-shaped body, which is adapted to be in secure contact with one of said inner guide surfaces of said pair of uprights of said outer mast and the surfaces of said pair of bracket plates. 
 
     
     
       5. A mast assembly for a forklift truck, comprising:
 an outer mast including a pair of right and left uprights each mounted upright on the front of a truck frame of the forklift truck and each having inner guide surfaces; 
 an inner mast including a pair of right and left uprights each received in the corresponding one of said pair of right and left uprights of said outer mast for elevational movement and each having inner guide surfaces and outer guide surfaces; 
 a carriage assembly having a pair of right and left bracket plates each received in the corresponding one of said pair of right and left uprights of said inner mast for elevational movement; 
 a first guide unit fixed onto said inner guide surfaces of each said upright of said outer mast and being in contact with said outer guide surfaces of the corresponding said upright of said inner mast so as to guide said inner mast for elevational movement; 
 a second guide unit fixed onto said outer guide surfaces of each said upright of said inner mast and being in contact with said inner guide surfaces of the corresponding said upright of said outer mast so as to guide said inner mast for elevational movement; and 
 a third guide unit fixed onto each said bracket plate and being in contact with said inner guide surfaces of the corresponding said upright of said inner mast so as to guide said carriage assembly for elevational movement;
 wherein at least one of said first, second, and third guide units comprises a sliding pad member made of a plastic material, and said sliding pad has a hollow, block-shaped body, which is open at its base side, said block-shaped body having a rectangular shaped cross section and includes a first pair of opposing side walls and a second pair of opposing side walls, a plain front wall which is provided at the side of said block-shaped body opposite to said base side, and the sliding pad has an outer surface defining a rectangular sliding contact surface, which is to be in sliding contact with one of said outer guide surfaces of said pair of uprights of said inner mast, said inner guide surfaces of said pair of uprights of said outer mast, and said inner guide surfaces of said pair of uprights of said inner mast; and 
 
 the sliding pad member further includes a pair of reinforcement ribs formed on an inner surface of said front wall and extending along diagonal lines of the rectangular sliding surface and crossing at the center of the rectangular sliding surface; and 
 the sliding pad further includes a pair of grooves for holding lubricant formed in the sliding contact surface and extending along the pair of reinforcement ribs; and 
 and the sliding pad member further includes a pair of ring-shaped tabs, each tab having a through hole, and one tab is formed within each wall of the first set of opposing side walls of said block-shaped body for fixing said block-shaped body, by means of a screw, onto one of said inner guide surfaces of said pair of uprights of said outer mast, said outer guide surfaces of said pair of uprights of said inner mast, and the surfaces of said pair of bracket plates and the head of the fixing screw is at a level lower than that of the sliding contact surface.